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Several COVID-19 vaccines have recently gained authorization for emergency use. Limited knowledge on duration of immunity and efficacy of these vaccines is currently available. Data on other coronaviruses after natural infection suggest that immunity to SARS-CoV-2 might be short-lived, and preliminary evidence indicates waning antibody titers following SARS-CoV-2 infection. In this work, we model the relationship between immunogenicity and protective efficacy of a series of Ad26 vectors encoding stabilized variants of the SARS-CoV-2 Spike protein in rhesus macaques and validate the analyses by challenging macaques 6 months after immunization with the Ad26.COV2.S vaccine candidate that has been selected for clinical development. We show that Ad26.COV2.S confers durable protection against replication of SARS-CoV-2 in the lungs that is predicted by the levels of Spike-binding and neutralizing antibodies, indicating that Ad26.COV2.S could confer durable protection in humans and immunological correlates of protection may enable the prediction of durability of protection., Several COVID-19 vaccines have received emergency approval, but durability of protection is unclear. Here, the authors describe correlates of protection (CoP) for the Ad26.COV2.S vaccine in rhesus macaques and report that CoP predict the protection observed 6 months post vaccination.

Pharmacokinetic/pharmacodynamic (PK/PD) models for hematological drug effects exist that assume that cells are produced by a zero- or first-order process, survive for a specific duration (cell lifespan), and then are lost. Due to the fact that delay differential equations (DDE) are needed for cell lifespan models, their software implementation is not straightforward. Our objective is to demonstrate methods to implement three different cell lifespan models for dealing with hematological drug effects and to evaluate the performance of NONMEM to estimate the model parameters. For the basic lifespan indirect response (LIDR) model, cells are produced by a zero-order process and removed due to senescence. The modified LIDR model adds a precursor pool. The LIDR model of cytotoxicity assumes a three-pool indirect model to account for the cell proliferation with capacity-limited cytotoxicity followed by maturation, and removal from the circulation. A numerical method (method of steps) implementing DDE in NONMEM was introduced. Simulation followed by estimation was used to evaluate NONMEM performance and the impact of the minimization algorithm (first-order method vs. first-order conditional estimation method) and the model for residual variability on the estimates of the population parameters. The FOCE method combined with log-transformation of data was found to be superior. This report provides methodology that will assist in application of population methods for assessing hematological responses to various types of drugs.

Purpose: R115777 is a selective nonpeptidomimetic inhibitor of farnesyltransferase (FTase), one of several enzymes responsible for posttranslational modification that is required for the function of p21ras and other proteins. Given that RAS mutations are nearly universal in pancreatic cancer and R115777 demonstrated preclinical activity against pancreatic cell lines and xenografts, this phase II study was undertaken to determine its clinical activity and effect on target proteins in patients with measurable metastatic pancreatic adenocarcinoma. Patients and Methods: Twenty patients who had not received prior therapy for metastatic disease were treated with 300 mg of R115777 orally every 12 hours for 21 of 28 days. Inhibition of FTase activity in peripheral-blood mononuclear cells was measured using a lamin B C-terminus peptide as substrate. Western blot analysis was performed to monitor farnesylation status of the chaperone protein HDJ-2. Results: No objective responses were seen. Median time to progression was 4.9 weeks, and median survival time was 19.7 weeks. The estimated 6-month survival rate was 25%, with no patients progression-free at 6 months. Grade 3/4 toxicities were liver enzyme elevation, anemia, neutropenia, thrombocytopenia, fatigue, nausea/vomiting, rash, and anorexia. FTase activity (mean ± SD) decreased by 49.8% ± 9.8% 4 hours after treatment on day 1 and 36.1% ± 24.8% before treatment on day 15. HDJ-2 farnesylation (mean ± SD) decreased by 33.4% ± 19.8% on day 15. Conclusion: Although treatment with R115777 resulted in partial inhibition of FTase activity in mononuclear cells, it did not exhibit single-agent antitumor activity in patients with previously untreated metastatic pancreatic cancer.